A newborn presents with delayed meconium passage, abdominal distension, and bilious vomiting. What is the most concerning diagnosis?

Correct Answer: C

Rationale: Hirschsprung disease is caused by the absence of ganglion cells in the distal colon, leading to functional obstruction, delayed meconium passage, and bilious vomiting. Diagnosis is confirmed with a rectal biopsy.

Correct Answer: D

Rationale: The statement 'Isoimmune hemolytic disease may be found in first-born infants irrespective of infant blood group' is incorrect. Isoimmune hemolytic disease typically occurs when maternal antibodies cross the placenta and attack fetal red blood cells. This is more common in subsequent pregnancies due to sensitization during the first pregnancy.

Correct Answer: A

Rationale: Methotrexate primarily works by suppressing the immune system, reducing inflammation in rheumatoid arthritis.

Correct Answer: A

Rationale: Hypertrophic cardiomyopathy primarily affects diastolic function, impairing ventricular filling despite normal systolic contraction.

Correct Answer: A

Rationale: Rumination is not seen exclusively in infants and those with intellectual disability; it can occur in other populations as well.